This invention relates generally to apparatus and methods for lifting, supporting and stabilizing generally horizontal structures overlying a ground surface. More particularly, this invention pertains to apparatus useful in confined spaces for raising, supporting and stabilizing floor slabs and the like.
Structures such as dwellings, industrial and business buildings, etc. are subject to settling and structural deformation from unstable ground conditions. Such deformation results when the soil and subsoil differentially expand and contract because of cyclical freezing and thawing, as well as from changes in moisture content. Some geographical areas have soils which are particularly susceptible to differential movement.
Various equipment and methods for shoring and stabilizing a sagging or settling building foundation are well known.
One method which has been used is the pressurized pumping of a grout material under a building slab or foundation to lift the settled structure. Usually, the subsoil continues to expand and contract, however, and the remedy is merely temporary.
In a more recent development, a tubular piling is driven beneath or adjacent the foundation. As the piling reaches bedrock or a highly resistant soil layer, the upward reaction forces on the pile driver are directed against the bottom surface of the foundation to lift it. A bracket attached to the piling remains permanently under the foundation for continued support thereof, enabling removal of the pile driver. Typically, a plurality of pilings is driven at 6-12 foot intervals along the foundation. Such systems are typified in U.S. Pat. Nos. 3,902,326 of Langenbach, Jr. and 4,673,315 of Shaw, et al. which disclose systems having a power cylinder above or alongside the foundation level for driving the piling. In the latter reference is disclosed the lifting of a slab from the building exterior; thus, the slab must extend to the outside wall of the building for accessibility. U.S. Pat. Nos. 4,708,528 of Rippe and 3,902,326 of Langenbach, Jr. disclose apparatus for lifting slabs from the interior of buildings by hydraulic pile drivers.
The lifting of slabs of concrete or other materials differs from the lifting of foundations. Typically, such slabs have a much higher ratio of horizontal surface area to vertical thickness than foundation members. The load placed on the pile driver is considerably less because the slab is thinner and normally does not support a building structure as does a foundation. Although the reduced load permits a more. distant spacing of the supportive piling, the propensity for the slab to crack under localized lifting forces may make wider spacing unworkable. Piling locations must be carefully selected to ensure adequate support of the slab over its entire area during and following the lifting operations. This support must continue after the slab has been restored to the desired elevation. The space between the lifted slab and the ground may be filled with gravel, sand or hardenable mortar materials of various types. Prior art practice resulted in relatively local support rather than support over the entire slab, or nearly so.
Another difference between foundations and slabs exists. Slabs are not generally accessible from the exterior of a building, so the piling must be driven through holes in the slab itself. From a structural standpoint, it is desirable to limit the size of such holes. The prior art practice of forming holes sufficiently large to excavate a hole beneath the slab and install a bracket or lifting plate in the hole under the slab, as disclosed in U.S. Pat. No. 4,800,700 to May, resulted in holes having typical dimensions of 1-3 feet. Such large holes severely weaken the slab.